<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        * {
            margin: 0px;
            padding: 0px;
            list-style: none;
        }

        .bg {
            width: 100vw;
            height: 100vh;
            background: #049ec4 url(cloud.jpg) repeat-x left bottom;
            animation: move 20s linear infinite;
        }

        @keyframes move {
            from {
                background-position-x: 0
            }

            to {
                background-position-x: -600px
            }
        }
    </style>
</head>

<body>
    <div class="bg"></div>
</body>

</html>